The present invention generally relates to cooling apparatus for torque transmitting units and drives of the type wherein a fluid sump contained within a housing is heated by the generation of heat energy during operation of relatively movable torque transmitting members connected between an input shaft and an output member.
The types of drives of concern herein are employed to control the speed of the output member in relation to that of the input shaft, and they are generally characterized by a relative speed difference or slip between the torque transmitting members which results in the generation of heat energy and the heating of the fluid in the drive housing. In a disc type torque transmitting unit, such as a clutch or a brake, heat is primarily generated by mechanical losses in the engaging discs or disc pack as a result of slippage and friction developed during acceleration and deceleration of the load. When the torque transmitting unit is used in a constant slip application such as a tension or drag apparatus, large amounts of frictional heat are continuously generated. In these instances, the clutch may be operated in the sump as a fluid bath to enhance heat dissipation, and the unit is referred to as a wet application. The high rates of heat generation of concern herein are also present in hydroviscous drives which are continuous slip devices wherein the torque is transmitted by shearing a film of fluid intermediate adjacent discs. The hydrokinetic type drive is also characterized by high rates of heat generation in the torque transmission fluid. In this instance, an impeller rotor acts as a centrifugal pump to impart kinetic energy to the fluid and a runner or output rotor acts as a turbine using the kinetic energy to drive the output shaft. In all of the foregoing drives, it is apparent that the torque transmission fluid is supplied to the torque transmitting members from the sump and returned to the sump at an elevated temperature during the operation of the drive, and that the heat energy generated must be dissipated in order to assure satisfactory operation of the drive.
The dissipation of the heat developed during the operation of such torque transmitting devices is an important design factor of the drive. The overall temperature must be limited to prevent overheating of the system. Further, torque transmission is affected by temperature and a uniform temperature should be maintained in order to enhance the consistency of operation of the drive.
The prior art is exemplified by U.S. Pat. Nos. 3,696,898, 3,638,773 and 2,576,156 which illustrate disc type drives and cooling apparatus. In accordance with various prior art devices, pumps for circulating the torque transmission fluid to heat exchangers are located remote of the fluid sump contained in the housing. The pumps are connected to the fluid sumps by pump inlet pipes, and the pumps may be mounted within the housing for operation by the drive input shaft or they may be mounted externally of the drive housing and independently driven. In other applications, the prior art teaches the disposition of a heat exchanger within the drive housing and independently circulating a cooling liquid therethrough for providing liquid-liquid heat exchange to cool the torque transmission fluid. Further, the use of input shaft driven fans for blowing cooling air over the outside surface of the drive housing is disclosed in the prior art.
The prior art has not efficiently resolved the heat dissipation requirements in such drives. The prior art structures are typically of limited thermal capacity, and they have generally resulted in drive operation restrictions as well as special cooling apparatus structure which significantly increase the size and cost of the drive. To an extent, the deficiencies of the prior art structures have resulted from the fact that the fluid within the housing is in a highly agitated condition and contains relatively large amounts of entrained air as a result of the operation of the relatively moving torque transmitting members. In order to pump and circulate the fluid under these conditions, the prior art has generally resorted to the use of pump inlets disposed adjacent the lower and calmer regions of the sump in efforts to assure a more constant intake of fluid having a minimum amount of entrained air. This results in a suction head which the pump must work against, pipe friction losses, potential pump priming problems, and the costs and routing problems associated with the inlet piping in the housing. The mounting of the pump externally of the drive housing may not avoid the foregoing problems and such an arrangement will create additional fluid sealing considerations, require additional pump mounting structure, and result in a less compact system.
In other drive applications requiring high levels of heat dissipation, the prior art has frequently resorted to liquid-liquid heat exchanger systems which significantly increase the overall size and installation requirements for the drive and result in correspondingly significant cost increases. The disposition of such a heat exchanger within the drive housing also creates additional sealing problems and the risk of contaminating the torque transmission fluid, which typically comprises a viscous oil having particular viscosity characteristics, with the liquid coolant.